Endocrine Abstracts

Introduction: Cellular differentiation and development of germ cells critically depend on a coordinated activation and repression of specific genes. The underlying regulation mechanisms, however, are largely unknown. Here, we describe the interplay between two transcription factors to be critical for cell type-specific expression in testis.

Methods: We investigated the binding of CREMτ (cAMP response element modulator tau) and GCNF (germ cell nuclear factor) to DNA by Band Shift and ChIP assays. Cell-based assays of wild type and mutated versions were performed by reporter gene experiments. Protein-protein interactions were measured by GST-pull down and immunoprecipitation assays. Finally, in vivo relevance of the critical binding sites was monitored using a transgenic mouse model.

Results: In vivo, expression of the CREM/GCNF-driven transgene is detectable in haploid spermatids, but not in any somatic tissue or at any other stages during germ cell differentiation. CREMτ acts as an activator of gene transcription whereas GCNF suppresses this activity. Both factors compete for binding to the same DNA response element. Effective binding of CREM and GCNF highly depends on composition and epigenetic modification of the binding site. CREM and GCNF bind to each other via their DNA binding domains, indicating a complex interaction between the two factors. There are several testis-specific target genes that are regulated by CREM and GCNF in a reciprocal manner, showing a similar activation pattern as during spermatogenesis.

Conclusion: Our data indicate that a single common binding site for CREM and GCNF is sufficient to specifically direct gene transcription in a tissue-, cell type- and differentiation-specific manner.